Narrow filter for CW on a FT 840?

Discussion in 'General Technical Questions and Answers' started by MI0OIM, Jan 10, 2021.

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  1. MI0OIM

    MI0OIM Ham Member QRZ Page

    Hello purveyors of wisdom!

    I have just got a FT840.

    It doesn't have the narrow filter fitted, and as I play mainly on CW, I really like to address that.

    these things aren't available anymore so is there another way to do it?

    even filter the audio output?

    any suggestion welcom!

  2. NN4RH

    NN4RH Premium Subscriber QRZ Page

    MFJ Enterprises has some CW audio filters. They probably won't help if you've got nearby strong signals swamping the AGC of the radio but if there are signals in the passband that are merely annoying, then probably do a bit of good.

    I had an FT-840 back around 2001-2005. Just sort used the "filter between my ears"; i.e. if you can concentrate well enough you can learn to ignore all the other signals in the passband. I doubt I could operate that way now, too scatter-brained as I get older, but back then I even operated contests like that.

    Otherwise, if you are patient maybe a YF112c could show up on eBay or the QRZ swap meet some day. Might cost you $200. At some point you may have to give up and just get a better radio with IF DSP or SDR for better CW performance.
  3. NN4RH

    NN4RH Premium Subscriber QRZ Page

    I wonder if one could home-brew a small pc board to adapt a filter intended for some other radio into the FT-840? And if it'd be worth the trouble.
  4. KD1JT

    KD1JT Ham Member QRZ Page

    .................. suggested Inrad, but they're out of production there too
  5. K1MMI

    K1MMI Ham Member QRZ Page

    You might be able to find a used Timewave DSP filter on or ebay.

    On ebay you can search for FT-840 and at some point someone may be selling the YF-112C 500 Hz filter for the FT-840. Just double check the YF-112C is the correct model number for the 500Hz filter for the 840.

    You might be able to find a used Autek QF-1A SSB/CW/AM Filter for $50 to $75. On someone is selling the QF-1A shipped for $70.

    Plus you could search for INRAD filters on and ebay but I don't know what INRAD filters were sold for the FT-840.
    Last edited: Jan 10, 2021
  6. N3PM

    N3PM Ham Member QRZ Page

    Haven't seen the Inrad 119 or 120 on ebay for a looong time.
    Out of the three Timewaves that come up often, I found the DSP 59+ to deliver the best bang for the buck. The DSP-9 isn't as flexible and the top of the line DSP 599ZX is still a little costly and, in my mostly CW situation, many features aren't used.
    Mike N3PM
  7. WA9FZB

    WA9FZB XML Subscriber QRZ Page

    I had an FT-840 back some years ago. When I bought it (new) I also bought the 500 Hz mechanical filter. You may be able to locate one with a "Want to Buy" on the Swap Meet. Also, IIRC, Inrad used to make filters that fit the 840 as well.

    At the same time, I used an audio filter on the headphone line. There are loads of different ones out there, so maybe another WTB ad is called for. I had one that I built from a QST article, one Ramsey Kit (yuk!) and one MFJ (model 722, I think), that was actually quite helpful. There are other audio filters, like the Timewave, too.

    You probably have a better chance at finding an audio filter than you do an IF filter, though.

    I had a lot of fun with that rig on CW, even with just a vertical in the yard.
  8. KC3RN

    KC3RN Ham Member QRZ Page

    I don't know if they ship to the U.K., but you might want to consider this:

    It's a fun build, and works very well. It also has a limiter circuit, which helps keep static crashes and loud nearby stations under control. I usually use it on my TS-50, which, like your 840, has no mechanical filters in it.
  9. MI0OIM

    MI0OIM Ham Member QRZ Page

    lots of good stuff there folks, thanks a lot!

    I'm thinking an external audio filter of some kind is looking like the direction to go, so thanks!
  10. W4HWD

    W4HWD Premium Subscriber QRZ Page

    I second the Timewave DSP. I had one on a Kenwood TS-440s; it gives a plain low-end radio the selectivity of an expensive radio.

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